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General statistics on the distribution and suitability of Pinus cembra in the alps

The main objective of this exercise is to calculate the ha of tree cover for the distribution and Suitability of Pinus cembra. In this exercise we practice and learn some Bash shell scripting and awk commands within the grass environment.


For estimating the ha of Tree cover of Pinus cembra current distribution and suitability we are going to use and cross the following maps.

In the forest/non-forest map, the rescaled 25m to 1km resolution was done using a 0ha/1ha threshold for presence/absence reclassification to ensure inclusion of every hectare of forested landscape. This allows us to accurately determine areas of distribution and to estimate the suitability and distribution of Pinus cembra in its actual environment excluding lakes, water basins, agricultural landscapes, and urban and industrial areas.

Pinus Cembra distribution map: create a new GRASS location and define a region of analysis

Data preparation

We open a terminal and go to the directory corresponding to our GRASS LOCATION.

cd ~/ost4sem/grassdb/europe

We enter Grass in a pre-existing mapset

grass -text  ~/ost4sem/grassdb/europe/PCEM

Look at the default g.region and redefine a study area including only the Alpine mountain ranges. Set the new working region at 1km resolution and call it alpine

g.region -d
g.region -p
g.region n=2751000 s=2310000 w=3960000 e=4700000 res=1000 save=alpine --o
g.region -p

Create a new mapset

 g.mapset mapset=PCEMstat -c

Import the Euforgen Pinus cembra distribution map from the euforgen web page and convert it from a shape file to a raster file. Limit the import of polygons within the Alpine study area using the -r flag.

g.mapsets addmapset=PCEMstat
Import and reclass distribution map

Import the Euforgen Pinus cembra distribution map from the euforgen web page and convert it from a shape file to a raster file. Limit the import of polygons within the Alpine study area using the -r flag : -r dsn=~/ost4sem/exercise/rp_ratio/pcem_euforgen/Pinuscembra_LAEA.shp output=pcem_dist_alp --o

Data preparation

Convert the vector file to a raster file, look at the pixels values and reclass this map into a binary presence and absence of Pinus cembra distribution. --o input=pcem_dist_alp output=pcem_dist_alp use=cat pcem_dist_alp pcem_dist_alp
r.mapcalc pcem_dist_alp = "if(pcem_dist_alp > 0 , 1 ,0 )"
Estimate ha of tree cover in the the Euforgen data with the Pan European forest/non-forest map

Import the forest/non-forest map rescaled at 1km resolution -o -e input=~/ost4sem/exercise/rp_ratio/fnf_map/fnfp_1k/hdr.adf output=fnfpc

Generate a raster map of the forest area (percentage of area in 1 sq km) where Pinus cembra is distributed. The r.mapcalculator module of Grass allows you to calculate a new raster map from a r.mapcalc expression. r.mapcalc performs arithmetic on raster map layers. Look at: for more details.

r.mapcalculator amap=pcem_dist_alp bmap=fnfpc formula=A*B outfile=pcem_dist_infor --overwrite
The Pan-European forest/non-forest map rescaled at 1km resolution is a basic layer we might use in different projects within the Europe LOCATION. For this reason we are going to store it in the PERMANENT MAPSET, as detailed below:
g.mapset mapset=PERMANENT
g.mapsets addmapset=PCEMstat
g.copy rast=fnfpc@PCEMstat,fnfpc
g.mapset mapset=PCEMstat
g.remove fnfpc@PCEMstat

Pinus Cembra suitability map: data preparation

Import and resize suitability map

Import the random forest model of suitability for Pinus cembra.

The Modeled suitability map of Pinus cembra is stored in the
~/ost4sem/exercise/rpratio/pcemrandomforest/ folder -o  input=~/ost4sem/exercise/rp_ratio/pcem_randomforest/gdwarp_PRESENT.tif output=pcem_pot_alps --o

Resize the imported data at the Alpine study area. Since the function does not resize the map to the study area (it can only extend -e) we can use an r.mapcalc function. rmapcalc does include the resize option by default. pcem_pot_alps # check the extent
r.mapcalc pcem_pot_alps = "if(pcem_pot_alps >= 0,pcem_pot_alps, null())" pcem_pot_alps # re-check the extent
Generate the map of ha of forest suitability within the forested areas

Look at the pixel values in the pcempotalps map: pcem_pot_alps
d.mon start=x2
d.histogram map=pcem_pot_alps

You can also open Qgis and query zones to understand pixel values and their associated class. The map is composed of the following categories:

Pixel value category
1 Unsuitable areas
2 Suitable areas
20 Sea

We would like to have a binary map with the following reclassification:

Pixel value category
0 Unsuitable
1 Suitable

We have to reclassify the map. We can use the r.reclass function and use a text file containing the reclass rules. The reclasspotalps.txt file will be stored in the ~/ost4sem/exercise/pcemstat folder and has the following text:

1 = NULL
2 = 1
20 = NULL
 r.reclass input=pcem_pot_alps output=pcem_pot_no_pot_alps rules=~/ost4sem/exercise/pcemstat/reclass_pot_alps.txt --overwrite pcem_pot_no_pot_alps
 d.mon start=x2
 d.histogram map=pcem_pot_no_pot_alps

Generate a raster map of the forest area (percentage of area in 1 sq km) where Pinus cembra is suitable. We are going to multiply the reclassified suitability map for the forest/non-forest percentage map.

When we need to refer to a map stored in a different mapset from the current we can refer to the mapset with the syntax mapname@mapset_name
r.mapcalculator amap=pcem_pot_no_pot_alps bmap=fnfpc@PERMANENT formula=A*B outfile=pcem_suit_infor --overwrite

We now have ready the maps estimating ha of tree cover for the distribution and suitability of Pinus cembra The maps are respectively pcemdistinfor the former and pcemsuitinfor the latter.

Statistics of forested areas within the suitability and distribution maps

We are going to use grass and awk language for computing the sum of ha of forested areas.

Accumulated forested area within the climatically suitable zones for Pinus cembra to grow

the r.stat function include as option the -l and -c flags. -l : Print category labels and -c Print cell counts. Once we have extracted this information we will know the number of pixels per category. Each category corresponds to ha of forest per pixels. Multiplying (with awk) the category times pixels and summing the total multiplication results will estimate the ha of forest within suitable areas.

  r.stats -c -p -l -n input=pcem_suit_infor output=~/ost4sem/exercise/pcemstat/stat_suit.txt
  cd ~/ost4sem/exercise/pcemstat/
  awk '{  print $1 , $2 , $1*$2  }'  stat_suit.txt | awk '{ sum=sum+$3  } END { print sum }' > tot_ha_suit.txt   
Accumulated forested area within the Euforgen distribution map of Pinus cembra

The exact same procedure is carried out as above for the suitability.

  r.stats -c -p -l -n input=pcem_dist_infor output=~/ost4sem/exercise/pcemstat/stat_dist.txt
  awk '{  print $1 , $2 , $1*$2  }'  stat_dist.txt | awk '{ sum=sum+$3  } END { print sum }' > tot_ha_dist.txt 
the same info as r.stats are visible with the command -h -e map=pcem_dist_infor units=k


  • Casalegno S., G. Amatulli, A. Camia, A. Nelson, A. Pekkarinen. 2010. Vulnerability of Pinus cembra L. in the Alps and the Carpathian mountains under present and future climates. Forest Ecology and Management 259: 70-761.
  • Gaston 2003. The Structure and Dynamics of Geographic Ranges. Series: OXFORD SERIES IN ECOLOGY AND EVOLUTION. Kevin J Gaston 266 pages, Oxford University Press. ISBN-10: 0198526407.
  • Pekkarinen, A., Reithmaier, L. & Strobl, P. (2009): Pan-European forest/non-forest mapping with Landsat ETM+ and CORINE Land Cover 2000 data. ISPRS Journal of Photogrammetry and Remote Sensing 64: 171-183.
wiki/exercise_pcem_stats.txt · Last modified: 2021/01/20 20:36 (external edit)